Their challenge: use recent tech to create a stand-alone unit without piped-in water, a sewer connection, or outside electricity – all for less than 5 cents a day for a person to use.

“The present toilet is a 19th-century device that does not meet the needs of a vast part of the world’s population,” says Frank Rijsberman from the foundation. Flush toilets as we know it requires massive amounts of water and sewer infrastructure.

About 2.6 billion people without access to sewer-linked systems must use simple latrines, holes in the ground, or just the nearest available spot – which can lead to many health problems, like acute childhood diarrhea.

1. One new toilet is a compact chamber that runs on solar power from a roof panel and uses built-in electrochemical technology to process waste. Michael Hoffmann from Caltech received $400,000 to develop this solar toilet, which can be used up to 500 times a day. “We can clean the waste water up to the same level as would come out of a treatment plant,” he says.

It uses the sun’s energy to power an electrode system in the waste water; the electrodes drive a series of cleansing chemical reactions, converting organic waste in the water into carbon dioxide and producing hydrogen that can be stored in a fuel cell for night operation.

3. Some other groups are testing flush toilets that divert urine before it gets into the sewer. Dealing with urine separately, by siphoning it off to local storage tanks, simplifies waste water management. The urine can then be collected, treated, and recycled as fertilizer.

The Swiss Federal Institute of Aquatic Science and Technology (EAWAG) had a 6-year project on urine separation called No Mix technology. Each has a built-in urinal at the front that drains into storage, and the back compartment works like a conventional toilet with poop flushed into the sewer. (You need good aim for this to work.) EAWAG’s Tove Larsen led that project.

4. Larsen is also a Gates Foundation winner, but this time, she’ll be leading a team in developing a nonflush toilet. It will have separate compartments for urine and feces, along with a third compartment for water that is used to keep the toilet clean. After filtering, this water can be reused in the cleaning process.

“No innovation in the past 200 years has done more to save lives and improve health than the sanitation revolution triggered by invention of the toilet,” says Sylvia Mathews Burwell from the foundation. “But it did not go far enough. It only reached one-third of the world. What we need are new approaches. New ideas. In short, we need to reinvent the toilet.”

Financing will be given to one or more of the winning prototypes to be tested and produced commercially.

Janet Fang has written for Nature, Discover and the Point Reyes Light. She is currently a lab technician at Lamont-Doherty Earth Observatory. She holds degrees from the University of California, Berkeley and Columbia University. She is based in New York.
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